U.S. Pat. No. 4,647,576, which is herein incorporated by reference, discloses certain trans-6-[2-(substituted-pyrrol-1-yl)alkyl]pyran-2-ones.
U.S. Pat. No. 4,681,893, which is herein incorporated by reference, discloses certain trans-6-[2-(3- or 4-carboxamido-substituted-pyrrol-1-yl)alkyl]-4-hydroxy-pyran-2-ones.
The compounds disclosed in the above United States patents are useful as inhibitors of the enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA reductase) and are thus useful hypolipidemic and hypocholesterolemic agents. Particularly valuable as hypolipidemic and hypocholesterolemic agents are trans(.+-.)-5-(4-fluorophenyl)-2-(1-methylethyl)-N,4-diphenyl-1-[2-(tetrah ydro-4-hydroxy-6-oxo-2H-pyran-2-yl)ethyl]-1H-pyrrole-3-carboxamide and (2R-trans)-5-(4-fluorophenyl)-2-(1-methylethyl)-N,4-diphenyl-1-[2-(tetrahy dro-4-hydroxy-6-oxo-2H-pyran-2-yl)ethyl]-1H-pyrrole-3-carboxamide. The aforementioned compounds have been prepared by a linear synthetic route which employed two reactions conducted at low temperatures (-78.degree. C.) under carefully controlled conditions. The two reactions included the addition of ethyl acetoacetate to an aldehyde and the reduction of the hydroxy ketone produced in this reaction with sodium borohydride and a trialkylborane. Although these reactions provide the target compounds in high diastereomeric excess, they are difficult to conduct on large-scale and use expensive reagents which are difficult to handle. They also do not produce enantiomerically pure products. The materials produced by this method can be separated into enantiomerically pure products but the process is very expensive, time-consuming, and results in the loss of more than 50% of the starting material.
The aforementioned compounds have also been prepared by a linear synthetic route which employed two reactions conducted at low temperatures (-78.degree. C.) under carefully controlled conditions. The two reactions included the addition of the dianion of (S)-1,1,2-triphenylethanediol 2-acetate to an aldehyde and from the product conversion to the hydroxy ketone followed by the reduction of the hydroxy ketone produced in this reaction with sodium borohydride and a trialkylborane. Although these reactions provide the target compounds in high diastereomeric excess and reasonable enantiomeric excess (85:15), they are difficult to conduct on large-scale and use expensive reagents which are difficult to handle. Also, since an 85:15 ratio of enantiomers is produced, extensive chromatography is needed to isolate the desired enantiomer because the racemic product crystallizes leaving the desired isomer in the oily mother liquors. Both these linear procedures were published by Roth, et al, J Med Chem 1991;34:356-366.
The aforementioned compounds have also been prepared by a superior convergent route disclosed in the following U.S. Pat. Nos. 5,003,080; 5,097,045; 5,103,024; 5,124,482; and 5,149,837; which are herein incorporated by reference and Baumann K. L., Butler D. E., Deering C. F., et al, Tetrahedron Letters 1992;33:2283-2284.
One of the critical intermediates disclosed in U.S. Pat. No. 5,097,045 has also been produced using novel chemistry, as disclosed in U.S. Pat. No. 5,155,251, which is herein incorporated by reference and Brower P. L., Butler D. E., Deering C. F., et al, Tetrahedron Letters 1992;33:2279-2282.
The object of the present invention is an improved process for preparing the compounds described above by using a novel synthesis incorporating novel intermediates synthesized using novel chemistry.
Di-lithio and di-potassio-phenylacetamide and phenyl-acetanilide were reported in 1964 to react with ketones and methyl benzoate in liquid ammonia (Work S, Bryant D, Hauser C. R., J Org Chem 1964;29:722-724).
Solutions of .alpha.-sodio N,N-dimethylacetamide and some related .alpha.-sodio N,N-dialkylamides were reported in 1966 (Gassman P, Fox B, J Org Chem 1966;31:982-983 and Needles H, Whitfield RE, J Org Chem 1966;31:989-990).
Solutions of .alpha.-lithio N,N-dimethylacetamide and some related .alpha.-lithio N,N-dimethylamides were reported in 1977 (Hullot P, Cuvigny T, Larcheveque M, Normant H, Can J Chem 1977;55:266-273 and Woodbury R. P., Rathke M. W., J Org Chem 1977;42:1688-1690). These anions have been reacted as nucleophiles with highly reactive substances such as alkyl halides (iodides and bromides), epoxides, aldehydes and ketones. Reaction of these anions with esters appear to have been neglected or not reported. Two references to the reaction of acetamide with methyl benzoate, which proceed through the dianion of N-benzoylacetamide with methyl benzoate, have been found that yielded N-benzoyl benzoylacetamide (Structure A) at relatively high temperatures (Wolfe J, Timitsis G, J Org Chem 1968;33:894 and Agami C, Bull Soc Chim Fr 1968:1205). ##STR1##
We have unexpectedly and surprisingly found that while a solution of .alpha.-lithio N,N-dimethylacetamide does not yield any detectable desired product when reacted with (R) 5-cyano-3-hydroxybutyric acid alkyl esters (Formula A), solutions of .alpha.-metallo N,N-dialkylacetamide where at least one of the N,N-dialkyl substituents is larger than methyl or the N,N-dialkyl substituents together are cyclic, react at the ester group of (R) 5-cyano-3-hydroxybutyric acid alkyl esters (Formula A). ##STR2##
Thus, we have unexpectedly found a broad series of novel intermediates that can be used to synthesize the particularly valuable hypolipidemic and hypocholesterolemic agents trans (+)-5-(4-fluorophenyl)-2-(1-methylethyl)-N,4-diphenyl-1-[2-(tetrahydro-4-h ydroxy-6-oxo-2H-pyran-2-yl)ethyl]-1H-pyrrole-3-carboxamide and (2R-trans)-5-(4-fluorophenyl)-2-(1-methylethyl)-N,4-diphenyl-1-[2-(tetrahy dro-4-hydroxy-6-oxo-2H-pyran-2-yl)ethyl]-1H-pyrrole-3-carboxamide. Additionally, several of these intermediates may be used as oral prodrugs of the aforementioned hypolipidemic and hypocholesterolemic agents.